The invention is based on a fuel injection apparatus for internal combustion engines as defined hereinafter. In a fuel injection apparatus of this kind, known from an earlier German patent application number P 39 434 192 (U.S. Pat. No. 5,102,047), a pump piston axially guided in a cylinder bore of a pump housing is driven to reciprocate by a cam drive. With its face end remote from the cam drive the pump piston defines a pump work chamber in the cylinder bore into which a fuel supply line discharges and which is connected via a pressure conduit to an injection valve protruding into the combustion chamber of the internal combustion engine to be supplied. Both the quantity of fuel to be injected and also the beginning of the high-pressure delivery of the fuel found in the pump work chamber and therefore the beginning of the injection are regulated via the diversion process by means of a magnet valve that opens on either end, which is disposed in the fuel feed line, and which is controlled as a function of the operating parameters of the engine to be supplied.
Since the known unit fuel injector is driven mechanically via the cam drive as a function of the speed of the engine to be supplied, it has the disadvantage of a very steep increase of the injection pressure in the pump work chamber as the speed of the engine increases. The result, in a unit fuel injector design with an admissible maximum pressure at the nominal capacity point of the engine, or in other words at high engine speeds, is that the injection pressure in the lower speed range is not high enough. For an optimal combustion and the attendant low level of pollutant emissions, however, high injection pressures in the lower speed range are already necessary, which cannot be attained with the known unit fuel injector.